Method for thickening a cosmetic formulation using an alkali swellable emulsion of a polymer with amps and which is rich in acrylic acid

ABSTRACT

Process for thickening a composition, through the use of a direct emulsion in water, which is alkali-swellable, of a polymer of the ASE or HASE type, which is both rich in acrylic acid and which has a certain quantity of AMPS. The use of such emulsions simultaneously allows there to be no obligation to use surfactants and organic solvents other than water, and allows the thickening phenomenon to be activated for pHs of less than 7: this latter characteristic is particularly advantageous for formulations intended to be used in contact with skin.

REFERENCE TO PRIOR APPLICATIONS

This application claims priority to U.S. provisional application Ser.No. 61/452,733, filed Mar. 15, 2011; and to French patent application 1151812, filed Mar. 7, 2011, both incorporated herein by reference.

FIELD OF THE INVENTION

The present invention concerns a process for thickening a composition,preferably a cosmetic composition, through the use of a direct emulsionin water, which is alkali-swellable, of a polymer of the ASE or HASEtype, which is both rich in acrylic acid and which has a certainquantity of AMPS. The use of such emulsions simultaneously allows thereto be no obligation to use surfactants and organic solvents other thanwater, and allows the thickening phenomenon to be activated for pHs ofless than 7: this latter characteristic is particularly advantageous forformulations intended to be used in contact with human skin.

Additional advantages and other features of the present invention willbe set forth in part in the description that follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from the practice of thepresent invention. The advantages of the present invention may berealized and obtained as particularly pointed out in the appendedclaims. As will be realized, the present invention is capable of otherand different embodiments, and its several details are capable ofmodifications in various obvious respects, all without departing fromthe present invention. In this regard, the description herein is to beunderstood as illustrative in nature, and not as restrictive.

DISCUSSION OF THE BACKGROUND

Many cosmetic formulations are currently intended to be applied to skin:this is an intrinsic feature of beauty products, make-up products andbody-care products. It is sought, very naturally, to thicken suchformulations in a pH range matching that of skin, i.e. at values ofbetween 5 and 7, and preferentially between 5 and 6.5, and verypreferentially between 5.5 and 6.

There are a number of technical solutions to this problem, which may beclassified into 4 categories: use of polymers of higher molecularweights and in powder form, the technique called “back-acid”, whichrelies on acrylic polymers in direct emulsion of polymer particles inwater, use of other polymers, again in the form of direct emulsions, andfinally the use of reverse emulsions.

In the first category, one may cite document EP 1 138 703 A1, whichdescribes a cosmetic topical composition, including a polymer of highmolecular weight, with a base of at least one monomer having a freestrong acid group copolymerised with at least one esterified monomer andterminated by a hydrophobic group having 8 to 30 carbon atoms.

The abovementioned polymer is an emulsifying polymer, in solid form; itcan be dispersed in water and it enables the composition which containsit to be thickened, notably for pH values close to 5.

However, these polymers have the disadvantages relating to the use of apowder: difficulties of transport and cleaning, dangerousness of theproduct relating to its powdery, irritant and particular character. Inaddition, these polymers must be solubilised in the medium to bethickened, through the introduction of surfactants. The latterconstitute additional formulation additives which make the formulationmore complex, and which can interact with the surfactants alreadycontained in the formulation, sometimes creating undesirable effects(notably phase separation, or the formation of residual insolubles).

The technique called “back-acid” is also known, as described in documentWO 01/76 552. This is a method consisting in introducing a surfactantand an alkali-swellable acrylic copolymer into an aqueous medium. Thisleads to a thickening effect when its carboxylic acid groups areneutralised: a three-dimensional network is then created which leads toan increase of the viscosity of the aqueous phase. Such an effect may beactivated in a pH area close to 6, the role of the surfactant being tomaintain the thickening effect, even when the pH is reduced.

In addition to the abovementioned ion mechanism, there is an associativemechanism, based on the presence of a hydrophobic monomer: this is whatis described by document WO 03/62 288, which also seeks to thickenformulations with an acidic pH. The same goes for document U.S. Pat. No.4,529,773 A1. As with the back-acid method, the presence of a surfactantin the form of an additional product is therefore necessary, leading tothe previously mentioned disadvantages.

A number of documents which describe the use of other polymers inemulsion are also known. In this respect, document EP 0 824 914 B1describes a polymer containing an aminated cationic monomer. The soughtthickening effect will be obtained with an acidic pH through ionisationof the aminated cationic monomer. In document WO 2004/024 779, thecationicity of the envisaged polymer is provided by a substituted aminovinylic monomer. With this case also it is possible to thicken anaqueous medium with an acidic pH.

However, the toxicity of cationic polymers for aquatic fauna is wellknown: and they are unfortunately found at the life-cycle end in ourrivers, both large and small, into which they are discharged through thedomestic water system.

Finally, reverse emulsions and their applications as thickening agentsin the cosmetics field are also known, as disclosed in documents WO 2004063228 A1 and GB 2 422 605 A1. However, these structures require thepresence of surfactants and solvents to ensure their stability, and thedisadvantages mentioned above are then posed.

SUMMARY OF THE INVENTION

In continuing their research with a view to thickening aqueouscompositions, notably with pHs of less than 7, whilst overcoming thedisadvantages of the methods of the prior art, the inventors havedeveloped a thickening method using original structures. These aredirect emulsions in water of alkali-swellable (meth)acrylic polymers,three characteristics of which are:

-   -   absence of surfactants and organic solvents other than water,    -   majority presence of acrylic acid compared to methacrylic acid,    -   and the presence of a quantity of a particular monomer which is        2-acrylamido-2-methylpropane sulfonic acid (or AMPS, CAS no:        40623-75-4).

These products advantageously enable a formulation to be thickened,without however introducing new surfactants, or organic solvents otherthan water, into the formulation. In addition, it is possible toactivate the thickening phenomenon in a pH zone of between 5 and 7,without using the “back-acid” technique.

There was no knowledge of how to produce alkali-soluble emulsions whichwere rich in acrylic acid and free of surfactants and organic solventsother than water, before the importance of AMPS in such emulsions wasdiscovered. It is the presence of a certain quantity of the latter whichallows such products to be produced, with the previously mentionedattractions, which are particularly advantageous in the field ofcosmetics, notably in order to thicken formulations with a pH of lessthan 7, notably between 5 and 6.5, and more preferentially between 5.5and 6. These emulsions were described for the first time in FrenchPatent Applications which have been filed as numbers FR 10 55080 and FR10 55077, both incorporated herein by reference.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 shows the results of tests where the change in the Brookfield™viscosity in mPa·s of a gel (Y axis) was measured as a function of thepH (X axis).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein the expression “direct emulsion of a polymer in water”designates a stable and uniform dispersion of polymer particles in water(no reference is made here to emulsions of the oil-in-water orwater-in-oil type, which imply the existence of two separate phases, onewater-based and the other oil-based). Concerning the expression“alkali-swellable polymer”, it signifies that the polymer is capable,when the medium is alkaline, of incorporating a quantity of water suchthat there is formation of a gel and therefore an increase of viscosity.

The emulsions referred to in the present invention cover two majorfamilies of thickening agents: those of the ASE type (Alkali-SwellableEmulsion) and those of the HASE type (Hydrophobically modifiedAlkali-Swellable Emulsion). The former designate copolymers of(meth)acrylic acid with a non-water-soluble ester of these acids, andthe latter designate copolymers with a (meth)acrylic acid base of anon-water-soluble ester of (meth)acrylic acid and of a monomer havinghydrophobic groups called “associative” groups. These copolymers canalso be cross-linked.

The action mechanisms of these products, and notably thealkali-swellable character of these emulsions and their ability tothicken an aqueous medium with a pH close to neutrality, have beendescribed in documents WO 2007/144721 and “Practical guide toassociative thickeners” (Proceedings of the Annual Meeting TechnicalProgram of the FSCT, 2000, 78th, 644-702). Thickening agents of the ASEand HASE type are generally manufactured in the form of direct emulsionsof the alkali-swellable polymer in water, the active product content ofwhich varies between 10% and 45% of their total weight.

The corresponding synthesis method is notably described in the followingpublications: “Synthesis of an alkali-swellable emulsion and its effecton the rate of polymer diffusion in poly(vinyl acetate-butyl acrylate)latex films” (Journal of Polymer Science, Part A: Polymer Chemistry,2005, 43 (22), pp. 5632-5642), “Structural and rheological properties ofhydrophobically modified alkali-soluble emulsion solutions” (Journal ofPolymer Science, Part B: Polymer Physics, 2002, 40(18), pp. 1985-1994).It is also the subject of many patent applications (EP 0 089 213 A1, EP0 646 606 A1, EP 0 979 833 A1 in respect of ASEs and EP 0 013 836 A1, WO93/2454 A1, U.S. Pat. No. 4,268,641 A1, U.S. Pat. No. 4,421,902 A1, U.S.Pat. No. 3,915,921 A1 in respect of HASEs).

One object of the present invention is a method for thickening acosmetic formulation, through contact of the formulation with a directaqueous emulsion of a polymer, followed by regulation of the pH to avalue between 5 and 7, preferentially between 5 and 6.5, and verypreferentially between 5.5 and 6, wherein the emulsion is free fromsurfactants and organic solvents other than water, and in that thepolymer comprises, consists essentially of, or consists of, expressed asa % by weight of each of the monomers:

-   -   a) 20% to 60% by weight of methacrylic acid and acrylic acid,    -   b) 40% to 80% by weight of at least one monomer chosen from        among ethyl acrylate, butyl acrylate, methyl methacrylate and        their blends,    -   c) 0.05% to 22% by weight of 2-acrylamido-2-methylpropane        sulfonic acid,    -   d) 0 to 1% by weight of at least one cross-linked monomer, where        the total a)+b)+c)+d) equals 100%,

or

-   -   a) 20% to 60% by weight of methacrylic acid and acrylic acid,    -   b) 40% to 80% by weight of at least one monomer chosen from        among ethyl acrylate, butyl acrylate, methyl methacrylate and        their blends,    -   c) 0.5% to 25% by weight of a monomer containing a hydrophobic        group,    -   d) 0.05% to 22% by weight of 2-acrylamido-2-methylpropane        sulfonic acid,    -   e) 0 to 1% by weight of at least one cross-linked monomer, where        the total a)+b)+c)+d)+e) equals 100%,

where in both cases the % by weight of acrylic acid compared to thetotal weight of the acrylic and methacrylic acids is between 50% and100%, preferentially between 80% and 100%, very preferentially between98% and 100%, and extremely preferentially where this % equals 100%(there is thus no methacrylic acid).

The first type of composition indicated above is an emulsion of the ASEtype which is rich in acrylic acid, and the second is an emulsion of theHASE type which is rich in acrylic acid.

In the polymers of the invention it is understood that the monomers thatmake up the polymers exist in polymerized form, but they arenevertheless commonly referred to as polymers containing monomers, inaccord with convention.

In the invention method a preferred embodiment is wherein the monomercontaining a hydrophobic group has the general formulaR—(OE)_(m)-(OP)_(n)—R′, where:

-   -   m and n designate integers of less than or equal to 150, at        least one of which is non-zero,    -   OE and OP designate respectively ethylene oxide and propylene        oxide,    -   R designates a polymerisable group, and preferentially the        methacrylate or methacrylurethane group,    -   R′ designates a hydrophobic group having at least 6 and at most        36 carbon atoms.

In the invention method a preferred embodiment is wherein thecross-linked monomer is chosen from among ethylene glycoldimethacrylate, trimethylolpropanetriacrylate, diallyl phtalate, allylacrylate, the allyl maleates, methylene-bis-acrylamide,methylene-bis-methacrylamide, tetrallyloxyethane, thetriallylcyanurates, the allylic ethers and the acrylic, methacrylic andmethacrylurethane esters obtained from polyols.

In the invention method a preferred embodiment is wherein the aqueousemulsion has a dry extract of between 10% and 50% by dry weight ofpolymer, compared to its total weight.

In the invention method a preferred embodiment is wherein the emulsionhas a particle size of between 50 nm and 500 nm.

In the invention method a preferred embodiment is wherein the polymerhas an average molar mass by weight of between 20,000 g/mole and1,000,000 g/mole.

In the invention method a preferred embodiment is wherein theformulation, preferably a cosmetic formulation, is chosen from among theforms containing at least one surfactant, and notably from among thoseintended to be applied to skin (care creams, make-up products, foamingagents, shampoos, etc.).

The following examples allow the invention to be better understood,without however limiting its scope.

EXAMPLES Example 1

This example relates to the thickening of water at a pH of 5.5.

3 emulsions of the HASE type according to the invention, using a polymerthe mass composition of which is given in table 1, were tested.

TABLE 1 Methacrylate Test n^(o) AA AMA AE C₂₂(OE)₂₅ AMPS 1 35.7 0.6 52.510 1.2 2 44.2 0.3 49.35 4.95 1.2 3 38.40 0.3 55.2 4.9 1.2 AA: acrylicacid AMA: methacrylic acid AE: ethyl acrylate Methacrylate C₂₂(OE)₂₅: amonomer of general formula R—(OE)_(m)—(OP)_(n)—R′, where m = 25, n = 0,OE and OP designate respectively ethylene oxide and propylene oxide, Rdesignates the methacrylate group, and R′ designates the linear alkylgroup having 22 carbon atoms AMPS: 2-acrylamido-2-methylpropane sulfonicacid

In the course of test no 4 a polymer sold by the company Lubrizol™ underthe name Aqua SF-1 was also used.

For each test, 1% by dry weight of the polymer for testing, compared tothe total weight of water to be thickened, was used. The change in theBrookfield™ viscosity in mPa·s of the gel, measured at 100 revolutionsper minute and at 25° C., was measured, as a function of the pH whichwas increased through the gradual addition of sodium hydroxide.

FIG. 1/1 shows this change in the case of tests no 1 (lozenges), 2(squares), 3 (crosses) and 4 (circles).

It can be seen clearly that the method according to the invention whichuses the emulsions with AMPS enables the thickening phenomenon to beactivated for much lower pH values than with the commercial polymer.

In addition, the thickening power in the pH zone between 5.5 and 6 isgreater in the case of the polymers of the invention than for thepolymer of the prior art.

In view of the above, a preferred embodiment of the invention herein isa method for thickening a formulation, comprising contacting theformulation with a direct aqueous emulsion of a polymer to form athickened formulation, followed by regulation of the pH of the thickenedformulation to a value between 5 and 7, wherein the emulsion is freefrom surfactants and organic solvents other than water and the polymerconsists, expressed as a % by weight of each of the monomers therein,of:

-   -   a) 20% to 60% by weight of methacrylic acid and, optionally,        acrylic acid where the % by weight of acrylic acid compared to        the total weight of acrylic and methacrylic acid is at least        50%,    -   b) 40% to 80% by weight of at least one monomer chosen from        among ethyl acrylate, butyl acrylate, and methyl methacrylate,    -   c) 0.05% to 22% by weight of 2-acrylamido-2-methylpropane        sulfonic acid, and    -   d) 0 to 1% by weight of at least one cross-linked monomer,

or

-   -   a) 20% to 60% by weight of methacrylic acid and, optionally        acrylic acid, where the % by weight of acrylic acid compared to        the total weight of acrylic acid and methacrylic acid is at        least 50%,    -   b) 40% to 80% by weight of at least one monomer chosen from        among ethyl acrylate, butyl acrylate, and methyl methacrylate,    -   c) 0.5% to 25% by weight of a monomer comprising a hydrophobic        group,    -   d) 0.05% to 22% by weight of 2-acrylamido-2-methylpropane        sulfonic acid, and    -   e) 0 to 1% by weight of at least one cross-linked monomer.

The above written description of the invention provides a manner andprocess of making and using it such that any person skilled in this artis enabled to make and use the same, this enablement being provided inparticular for the subject matter of the appended claims, which make upa part of the original description.

As used herein, the words “a” and “an” and the like carry the meaning of“one or more.” The phrases “selected from the group consisting of,”“chosen from,” and the like include mixtures of the specified materials.Terms such as “contain(s)” and the like are open terms meaning‘including at least’ unless otherwise specifically noted.

All references, patents, applications, tests, standards, documents,publications, brochures, texts, articles, etc. mentioned herein areincorporated herein by reference. Where a numerical limit or range isstated, the endpoints are included. Also, all values and subrangeswithin a numerical limit or range are specifically included as ifexplicitly written out.

The above description is presented to enable a person skilled in the artto make and use the invention, and is provided in the context of aparticular application and its requirements. Various modifications tothe preferred embodiments will be readily apparent to those skilled inthe art, and the generic principles defined herein may be applied toother embodiments and applications without departing from the spirit andscope of the invention. Thus, this invention is not intended to belimited to the embodiments shown, but is to be accorded the widest scopeconsistent with the principles and features disclosed herein. In thisregard, certain embodiments within the invention may not show everybenefit of the invention, considered broadly.

1. A method for thickening a formulation, the method comprising:contacting the formulation with a direct aqueous emulsion of a polymer,followed by regulating a pH of the formulation to a value between 5 and7, thereby forming a thickened formulation, wherein the emulsion is freefrom surfactants and organic solvents other than water and the polymerconsists, expressed as a content by weight of monomers therein, of: a)from 20% to 60% by weight of methacrylic acid, acrylic acid, or acombination thereof, wherein a content by weight of acrylic acid, ifpresent, compared to a total weight of acrylic and methacrylic acid isat least 50%, b) from 40% to 80% by weight of at least one monomerselected from the group consisting of ethyl acrylate, butyl acrylate,and methyl methacrylate, c) from 0.05% to 22% by weight of2-acrylamido-2-methylpropane sulfonic acid, and d) from 0 to 1% byweight of at least one cross-linked monomer. 2-3. (canceled)
 4. Themethod according to claim 1, wherein the cross-linked monomer isethylene glycol dimethacrylate, trimethylolpropanetriacrylate, diallylphtalate, allyle acrylate, an allyl maleate, methylene-bis-acrylamide,methylene-bis-methacrylamide, tetrallyloxyethane, a triallylcyanurate,an allylic ether, an acrylic ester obtained from a polyol, a methacrylicester obtained from a polyol, a methacrylurethane ester obtained from apolyol, or any combination thereof.
 5. (canceled)
 6. The methodaccording to claim 1, wherein the aqueous emulsion has a dry extract ofbetween 10% and 50% by dry weight of polymer, compared to its totalweight.
 7. The method according to claim 1, wherein the emulsion has aparticle size of between 50 nm and 500 nm.
 8. The method according toclaim 1, wherein the polymer has an average molar mass by weight ofbetween 20,000 g/mole and 1,000,000 g/mole.
 9. The method according toclaim 1, wherein the content by weight of acrylic acid compared to thetotal weight of the acrylic acid and methacrylic acid is from 80% to100%.
 10. The method according to claim 1, wherein where the content byweight of acrylic acid compared to the total weight of the acrylic acidand methacrylic acid is from 98% to 100%.
 11. The method according toclaim 1, wherein the polymer does not comprise acrylic acid. 12.(canceled)
 13. The method according to claim 1, wherein the formulationis a cosmetic formulation.
 14. The method according to claim 13, whereinthe cosmetic formulation comprises a surfactant and is suitable forapplication to human skin.
 15. (canceled)
 16. The method according toclaim 1, wherein the formulation has a pH of from 5 to 6.5 afterthickening.
 17. The method according to claim 11, wherein theformulation has a pH of from 5.5 to 6 after thickening.